answer should come out to be 816 but i keep getting the wrong answer. not sure what im doing wrong in the formula

PROGRAMMING: PERMUTATIONS ASSIGNMENT INSTRUCTIONS OVERVIEW Using the double variable type, you will create a program that uses two variables to calculate the number of permutations of the potential team arrangements. INSTRUCTIONS The number of permutations of a set of n items taken r at a time is given by the following factorial of the result of nr. The factorial of a number n can be solved using the following formula: n!=ennn2n. If there are 18 people in your class and you want to divide the class into programming teams of 3 members, you can compute the number of different teams that can be arranged using this formula (n!/r!(nr)!). Write a C++ program that determines the number of potential team arrangements. You will need to use the double type variable for this computation. 1. Copy the Lab Template from the lab submittal instructions to fa new blank c++ file. Use the file as the foundation of your program. 2. Add the variables \& math computations necessary to complete the calculations. 3. Output the results to the screen. The output must be labeled clearly and formatted neatly. 4. Include proper formatting, and appropriate comments in your code. More commentsinside for the programmer and outside for the user = better grades